1. Field of the Invention
The present invention relates generally to a wireless communication system, and in particular, to a coding technique with maximum diversity gain in a multiple antenna transmission system.
2. Description of the Related Art
As a way to improve the performance of mobile communication systems under a fading channel environment, many studies have been conducted on transmit antenna diversity with which data is transmitted through multiple antennas. Transmit antenna diversity, which provides diversity gain using a plurality of transmit antennas, is suitable for future-generation high-speed data communication. To achieve the transmit antenna diversity gain, various channel coding techniques have been proposed.
Orthogonal space-time block codes (STBCs) that are based on an orthogonal design theory is one example of a technique of achieving optimum transmit antenna diversity gain. The orthogonal STBCs advantageously have a maximum diversity order and enable maximum likelihood (ML) decoding through simple linear processing on a receiver side.
However, the orthogonal STBCs, without using additional frequency bands, exist for an arbitrary number of antennas for pulse amplitude modulation (PAM), and exist only for two transmit antennas for quadrature amplitude modulation (QAM).
Aside from the orthogonal STBCs, a new full rate diversity structure has been proposed that provides maximum diversity gain in QAM, under a Raleigh fading channel environment. This diversity structure achieves spatial diversity gain by rotating the constellation of QAM modulation symbols through a constellation-rotating pre-coder and interleaving the resulting symbols. A full rate space-time constellation-rotating code was proposed by modifying the diversity structure. Signals from the constellation-rotating pre-coder are transmitted through a plurality of transmit antennas for different symbol periods such that they separately experience fading.
However, the full rate space-time constellation-rotating codes are not orthogonal and increase ML detection complexity for detecting the space-time constellation-rotating codes exponentially in proportion to the number of transmit antennas and the size of the symbol constellation.